This study evaluates the applicability of Demirjian and Willems’ methods for age estimation in Portuguese children aged 6–9 years based on orthopantomographs (OPGs). The main objective was to compare the precision of both methods in estimating chronological age (CA). This study analyzed 160 OPGs, equally distributed by sex, and the dental age (DA) was calculated twice, using both methodologies. The findings reveal that Demirjian’s method consistently overestimated the chronological age by an average of 1.47 years for males and 1.45 years for females. Similarly, the Willems method also overestimated the age but to a lesser extent, with mean differences of 1.18 years for males and 0.91 years for females. Statistical analysis confirmed that both methods significantly overestimate age, with the most considerable discrepancies observed in 8-year-old individuals. Despite the Willems method providing slightly more accurate results, neither method was reliable, particularly for male subjects. This study highlights the need for further refinement of these methods, considering their tendency to overestimate age, especially in specific age groups. This research improves age estimation techniques in forensic and clinical settings, especially within the Portuguese pediatric population.